This invention is in the field of Boilers and Steam Generating Systems. Specifically, it is in the field of control of boilers.
In current industry practice, boilers are controlled in many different ways.
For example, to adjust the amount of boiler water treatment(s) added to minimize boiler corrosion, scale, or other problems, the following methods may be used.
Manual Control of a boiler means that boiler operators will manually change one or more of these items to vary the amount of treatment fed to a boiler: a positive displacement treatment pump stroke length (volume delivered per stroke), frequency of pump stroke (how many strokes per unit of time) for a positive displacement pump, the concentration of treatment active being delivered through a positive displacement pump. Also possible to vary is the selection of entirely different treatment program/product to be fed through the treatment pump(s). A limitation of manual control is that operator intervention and action is required to make a change in the targeted dosage (amount of) treatment added to the boiler.
A limited type of automated control of a boiler is possible using mass flow meters by monitoring the amount of treatment fed to a boiler to the total boiler feedwater or steam mass flow rate and/or by measuring the amount of treatment mass flow rate. The amount of treatment chemical fed to a boiler may be automatically adjusted by changing the treatment pump stroke length and/or by changing the treatment pump stroke frequency. Calibration errors, long-term reliability, and service requirements of mass flow meters in this type of automatic control scheme make it typically less accurate and frequently result in poorer control than with the inert tracer based approach listed above.
U.S. Pat. No. 5,041,386 describes a method involving automated control with an inert tracer through use of a boiler treatment product containing a tracer known to be inert under boiler conditions. With this method the dosage of a treatment may be automatically controlled by feedback or feedforward control of the treatment pump stroke length and/or treatment pump stroke frequency. The use of this inert tracer is the preferred automatic control method of boiler treatment dosage known in practice today.
To adjust the amount of boiler cycles of concentration the following actions may be used: for manual control, boiler operators will manually change one or more of the following items to vary the boiler cycles of concentration (described in U.S. Pat. No. 5,041,386). This method is conducted by using the following operating parameters:
Increase or decrease blowdown mass flow rate by changing the opening of the continuous blowdown valve.
Open the boiler bottom blowdown valve to decrease boiler cycles of concentration. This is almost always a discontinuous operation only done for short periods of time (seconds to minutes in length).
Increase or decrease the continuous blowdown sample flow rate to instruments and/or to the chemical analysis area to control the boiler cycles of concentration
For automatic control of a continuously operating boiler in order to adjust the boiler cycles of concentration it is necessary to vary the blowdown mass flow rate. Varying the blowdown mass flow rate is typically done in one of the following ways:
Measure and control blowdown conductivity and/or total dissolved solids continuously and adjust the blowdown valve opening to control the amount of boiler water conductivity. To increase cycles of concentration, the blowdown valve is closed which reduces the continuous blowdown mass flow rate. To decrease the cycles of concentration, the valve is opened which increases the continuous blowdown mass flow rate. The conductivity (or total dissolved solids) may or may not be continuously measured in the boiler feedwater to provide a numeric value of cycles of concentration (blowdown conductivity divided by feedwater conductivity).
Measurement and control blowdown inert tracer concentration (U.S. Pat. No. 5,041,386) continuously by adjusting the blowdown valve opening to control the amount of boiler water tracer concentration is also practiced. To increase cycles of concentration, the blowdown valve is closed which reduces the continuous blowdown mass flow rate. To decrease the cycles of concentration, the valve is opened which increases the continuous blowdown mass flow rate. The tracer concentration may or may not be continuously measured in the boiler feedwater to provide a numeric value of cycles of concentration (B lowdown tracer concentration divided by feedwater tracer concentration).
In some cases, the continuous control of cycles of concentration may be achieved by continuously measuring the blowdown mass flow rate. By comparing this mass flow rate versus the expected (targeted) total boiler feedwater, or by comparison to a continuously measured feedwater mass flow rate, the automatic adjustment of the continuous blowdown valve to control cycles can be achieved. Cycles of concentration is equal to the actual feedwater mass flow rate divided by the blowdown mass flow rate. Unfortunately, the accuracy of mass flow meters make this method many times less accurate in practice than the inert tracer method of automatic control listed above.
New methods of boiler control are always desirable.
The instant claimed invention is a method of controlling a boiler in which control is based on information from a control Matrix applicable to the specific operating parameters of said boiler comprising:
(i) providing a suitable fluorometer, sufficient analytical devices and a suitable controller;
(ii) programming said suitable fluorometer and controller using planning information from a control Matrix for boilers being treated with treatment programs selected from the group consisting of:
(a) Polymer Based All-in-One Product,
(b) Residual Phosphate Polymer Product with Scavenger and Condensate Corrosion Inhibitor Fed Separately; and
(c) pH/Phosphate Product with Polymer, Scavenger, and Condensate Corrosion Inhibitor Fed Separately;
(d) All-polymer Product with Separate Scavenger and Condensate Corrosion Inhibitor Fed Separately;
(e) pH/Phosphate Polymer Product with Scavenger and Condensate Corrosion Inhibitor Fed Separately;
(iii) using said fluorometer and sufficient suitable analytical devices to determine the status of system factors;
(iv) determining the pattern of changes in the readings from step (iii) over time;
(v) comparing the changes in readings in steps (iii) and (iv), with the patterns listed in the control Matrix to determine what corrective action(s) is recommended; and
(vi) using said controller to automatically implement said corrective action(s).